Serrated, like the teeth of a saw.
Serrulated, very minutely serrated.
Sessile, sitting or seated.
Seta, a bristle.
Setaceous, bristly, covered with bristles.
Setiferous, bearing bristles.
Setose, covered with bristles.
Sinister valve, is the left valve.
Sinus, a groove or cavity.
Siphunculus, a cylindrical canal perforating the partitions in polythalmous shells; for instance, as in the Nautilus Spirula.